My neighbor John and I got into a serious disagreement while working on a fence between our houses: will we use an English foot (John’s proposal) or a traditional Croatian elbow (my proposal) to measure the fence? This event helped me solve a problem that has plagued me since elementary school.

In elementary school we got instructions on how to manipulate units when calculating physical quantities: calculate with units in the same way as you calculate with variables in algebraic expressions. But why is this rule correct?

My answer is simple (and weird at a first glance): we can do it because of meter, kilogram, etc. ARE numbers. How did the disagreement between John and me end? How is it possible that the units of measurement and physical quantities are numbers? You can find answers here (Section 4.10 from my book Understanding and Doing Math): Units of Measurement

To convince the scientific community of the correctness of my solution, I had to formulate it in the form of a scientific article “A Simple Interpretation of Quantity Calculus” published in the journal Axiomathes: https://rdcu.be/cEqly